Android : Android crash when change text in EditText

I have a problem when change the text in EditText, my expected result is clear old text then set the new text that user input. After that, every working with editText is normal.

Exp: old text: 'abcdef',
     user press key 'k',
     expected text in editText is: 'k'

Here is my code:

editText.addTextChangedListener(new TextWatcher() {
private boolean firstRun = true;
@Override
public void onTextChanged(CharSequence s, int start, int before, int count) {
    if(firstRun) {
        editText.removeTextChangedListener(this);
        firstRun = false;
        if(count == 0) {
        // Delete key or other special key
            editText.setText("");
            return;
        } else {
            if(s.length() > start) {
                editText.setText(String.valueOf(s.charAt(start)));
                editText.setSelection(etp.getEditText().getText().length());
            } else {
                editText.setText("");
            }
        }
   }

}

My code is crashed in case user paste a new text inside old text (it's not crashed if user paste from begin or end of old text).

Exp: Old text: abcdef
     User action: abcd(paste here)ef

The logcat is below

08-14 06:18:55.977: E/AndroidRuntime(4187): FATAL EXCEPTION: main
08-14 06:18:55.977: E/AndroidRuntime(4187): java.lang.IndexOutOfBoundsException: replace (-1 ... -1) starts before 0
08-14 06:18:55.977: E/AndroidRuntime(4187):     at android.text.SpannableStringBuilder.checkRange(SpannableStringBuilder.java:1021)
08-14 06:18:55.977: E/AndroidRuntime(4187):     at android.text.SpannableStringBuilder.replace(SpannableStringBuilder.java:441)
08-14 06:18:55.977: E/AndroidRuntime(4187):     at android.text.SpannableStringBuilder.replace(SpannableStringBuilder.java:435)
08-14 06:18:55.977: E/AndroidRuntime(4187):     at android.text.SpannableStringBuilder.replace(SpannableStringBuilder.java:30)
08-14 06:18:55.977: E/AndroidRuntime(4187):     at android.widget.TextView.replaceText_internal(TextView.java:8442)
08-14 06:18:55.977: E/AndroidRuntime(4187):     at android.widget.TextView.prepareSpacesAroundPaste(TextView.java:8250)
08-14 06:18:55.977: E/AndroidRuntime(4187):     at android.widget.TextView.paste(TextView.java:8271)
08-14 06:18:55.977: E/AndroidRuntime(4187):     at android.widget.TextView.onTextContextMenuItem(TextView.java:8036)
08-14 06:18:55.977: E/AndroidRuntime(4187):     at android.widget.Editor$ActionPopupWindow.onClick(Editor.java:2862)
08-14 06:18:55.977: E/AndroidRuntime(4187):     at android.view.View.performClick(View.java:4204)
08-14 06:18:55.977: E/AndroidRuntime(4187):     at android.view.View$PerformClick.run(View.java:17355)
08-14 06:18:55.977: E/AndroidRuntime(4187):     at android.os.Handler.handleCallback(Handler.java:725)
08-14 06:18:55.977: E/AndroidRuntime(4187):     at android.os.Handler.dispatchMessage(Handler.java:92)
08-14 06:18:55.977: E/AndroidRuntime(4187):     at android.os.Looper.loop(Looper.java:137)
08-14 06:18:55.977: E/AndroidRuntime(4187):     at android.app.ActivityThread.main(ActivityThread.java:5041)
08-14 06:18:55.977: E/AndroidRuntime(4187):     at java.lang.reflect.Method.invokeNative(Native Method)
08-14 06:18:55.977: E/AndroidRuntime(4187):     at java.lang.reflect.Method.invoke(Method.java:511)
08-14 06:18:55.977: E/AndroidRuntime(4187):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
08-14 06:18:55.977: E/AndroidRuntime(4187):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
08-14 06:18:55.977: E/AndroidRuntime(4187):     at dalvik.system.NativeStart.main(Native Method)

Can you help me? Thanks !